Contact

Subscribe via Email

Subscribe via RSS

Categories

Creative Commons Attribution 4.0 International License
© Rakhesh Sasidharan

CSS2 selectors

Was working with CSS2 selectors today, thought I’d write a post about that.

Consider the following HTML code:

CSS selectors come into play when you want to select specific elements. For instance, suppose I had a CSS declaration such P { color: red; } it will apply to all P elements in the HTML – which may not be what I want. What if I wanted to target only the first P element instead? Or P elements following an H2 element? That’s when you’d use a selector. Selectors make use of relationships between elements.

Relationships

Every element in a given HTML code has a relationship to other elements in the code. It could be a child to another element, an adjacent sibling, the first child of an element, a grand child to an element, and so on. Below I have enumerated the elements from the HTML code above into a form that shows the elements and their relationships. Some elements have a + instead of | – this simply indicates the element is the first child of that type.

Child selectors

Child selectors are used to match elements that are children of another element. The > symbol is used to indicate a “child” relationship. Some examples:

  • LI > P { color: blue; } will target only those P elements that are children of an LI element.
  • OL > LI { color: blue; } will target only those LI elements that are children to OL elements but not UL elements.

Descendant selectors

Descendant selectors are used to match elements that are descendants of another elements. An element is a descendant of another element if it is a child of that element or if its parent is a descendant of that element (pretty obvious usage of the word, actually). A space between elements is used to indicate “descendancy”. Some examples:

  • P STRONG { color: blue; } will target only those STRONG elements that are descendant to a P element. This will not pick the STRONG element that is a child to H1 for instance.

While the child selector is for the immediate children – and does not select grand-children – the descendant selector includes children and grand-children. That’s the difference between these two operators.

Thus BODY > H1 will select all H1 elements that are a direct child of the BODY element – skipping the H1 element that is a child of DIV (hence a grand-child) – while BODY H1 will select the latter too.

If you want to select all descendants except the child – i.e. only the grand-children and further – the * symbol can be used instead of a space. Thus in the HTML code above, BODY * H1 { color: blue; } will skip the H1 elements that are children to the BODY element but target H1 elements that are children to the DIV element (as these are grand-children and descendants).

First child

Notice how I had marked many elements as the first children in my tree of HTML elements above. The reason I did that is because there’s a selector to target just the first children of an element. This is a pseudo-class actually – like how to add a :hover to match A elements when the mouse is hovering over it – so you add a :first-child to the element. Some examples:

  • P:first-child { color: blue; } will target only those P elements that are the first children of any element. In the HTML code above, this will match the P elements with the text “Hello and welcome to my page!” (first P element child of the BODY element) and “I love Batman!” (first P element child of the LI element).
  • Similarly, LI:first-child { color: blue; } will target only those LI elements that are the first children of any element.
  • It is possible to combine selectors too. BODY > P:first-child { color: red; } targets the first child from all the P element children of the BODY element while LI P:first-child { color: red; } targets the first child from all the P elements descendants of the LI element.

Adjacent sibling selectors

Adjacent sibling selectors are used to target siblings that are adjacent to each other. Two elements are siblings if they have the same parent (again, an obvious use of the word). Further, for this element to target such siblings, they must be adjacent to each other. Bear in mind the target is the second sibling, not the first. Some examples:

  • P + P { color: red; } will target all adjacent sibling P elements.
  • P:first-child + P { color: red; } will target all adjacent sibling P elements only if the first sibling is also the first-child. In the HTML code above only the “Here are some of the Batman villains” line matches this criteria.
  • LI:first-child + LI { color: red; } will target the second LI element of every first list.

See also

These are the main selectors. There are some more selectors – based on attributes of the elements and/ or language – best to refer to the W3 CSS2 selectors page for that.